Method of using a coke preheater

ABSTRACT

A method is described for preheating coke in a calcining process to a temperature between about 600* to 850* F. This preheating avoids shattering of the coke into undesirable small particles in the calcining kiln. The hot combustion gases from the kiln are admixed with air to burn all volatile combustible material contained in the gases and a portion of the resultant hot gases is admixed with cooler recycle gas from the preheater to obtain a heating gas for the preheater having a temperature between about 800* and 850* F. This heating gas is supplied to the preheater in sufficient volume to preheat the coke to above about 600* F. The coke is passed through the preheater and kiln at the kiln capacity feed rate, sufficient to provide a coke residence time in the kiln no greater than about 54 to 58 minutes.

United States Patent [151 3,677,533 Olover et al. [4 July 18, 1972 [54]METHOD OF USING A COKE PREHEA'I'ER Pnmary Exarmner.lohn J. CambyAttorney-Milton W. Lee, Richard C. Hartman, Lannas S. [72] lnventors:Robert K. Olover, San LUIS Oblspo; Henderson, Dean s df d and Robe"Strauss George L. Ford, Arroyo Grande. both of Cflhf- 57 ABSTRACT [73]Assign: c'momhv L05 A method is described for preheating coke in acalcining gdes process to a temperature between about 600 to 850 F. This[22] Filed; "h 8, 1971 preheating avoids shattering of the coke intoundesirable small particles in the calcining kiln. The hot combustiongases from PP ,122 the kiln are admixed with air to burn all volatilecombustible material contained in the gases and a portion of theresultant 52 hot gases is admixed with cooler recycle gas from the preaa g zg g heater to obtain a heating gas for the preheater having a tem-[58] Field Search i "58 R 52 perature between about 800 and 850 F. Thisheating gas is supplied to the preheater in sufficient volume to preheatthe 6 m" coke to above about 600 F. The coke is passed through the [s lR Cm preheater and kiln at the kiln capacity feed rate, sufficient to UNTED S E PATENTS provide a coke residence time in the kiln no greaterthan about 54 to 58 minutes. l,303,088 5/l9l9 McCaig et al ..263/32 R2,486,205 /1949 Prosk ..263/52 X 9 Claims, 2 Drawing Figures PatentedJuly 18, 1972 2 Sheets-Sheet 1 ATTORNEY METHOD OF USING A COKE ramm'maDESCRIPTION OF THE INVENTION The invention relates to improvements incoke calcination and, in particular, to improvements in preheating ofthe coke feed prior to the coke calcination.

Petroleum coke, such as produced by delayed coking operations, containssubstantial amounts of volatile combustible material, generally fromabout to weight percent. This volatile material renders the cokeunsuited for electrode manufacture and similar uses. It is commonpractice, therefore, to remove the volatile combustible material bycalcining the coke. The calcination is commonly performed by passing thecoke through a rotary kiln in contact with hot combustion gases to raisethe temperature of the coke sufficiently to reduce its volatilecombustible material content to less than about 1 percent. Calcinationtemperatures required to do this typically range from about 2,000 to2,600 F.

Many petroleum cokes when introduced into a calcining kiln tend torupture and shatter into small particles, a large percentage of whichare too small for subsequent use. It has been found that this tendencycan be by preheating the coke to a temperature greater than about 600 F.and preferably between about 650 and 1.000" F. in the absence of anoxidizing atmosphere prior to its introduction into the kiln. Thepreheating treatment has been found to be effective in limiting theshattering of the coke and has been in commercial use for several years;however, this use has been plagued with operating difficulties and,heretofore, has limited the coke rate through the kiln to less than itsdesign capacity.

Initial attempts to preheat the coke were made in a refractory linedpreheater which is similar to that designed for use with rotary limeburning kilns. The extended use of such a preheater for coke was foundto be fraught with difficuities, resulting from the combustibility ofthe coke and its volatiles, from air leaks into the preheater whichcaused combustion and explosions, and from the coking tendency ofvolatile matter released from the coke during preheating.

In the process, the coke is heated to the desired temperature by passinghot gases through the preheater in the absence of any oxygen. These hotgases are generated in an afierbumer where the gas efiluent from thekiln is contacted with air to burn the volatiles released in thecalcination step. A portion of the resulting hot combustion gases fromthe afterburner are passed to the preheater and the remainder aredischarged into a vent stack. These gases, atter contacting the coke inthe preheater are recycled, part to the preheater inlet and theremainder to the afterbumer, with the amount and proportion of therecycled gases being varied to control the temperature of the gasesintroduced into the preheater. The design and construction of apreheater that can function with gases laden with cokable volatilematerial has, until recently, plagued the commercial use of cokepreheating.

We found that the successful employment of a coke preheating step priorto calcination required that the afterburner combustion gases, which arecirculated through the preheater, do not contain any significant amountof coking precursors. The desired reduction of coking precursors in thecalciner exit gases was attained by introducing air into the aflerburnerin an amount sufficient to increase the temperature of the combustiongases exiting the aflerbumer to between about l,$00 and 2,000 F. Inaddition, we found that to avoid excwsive coke deposits from forming onthe equipment, the temperature of the gas to the preheater must be lessthan that temperature which would volatilize a significant amount, e.g.,about 1 percent, of volatile combustible material from the raw coke. Themaximum allowable temperature which can be employed depends upon thetype of coke in the preheater and its volatile combustible materialcontent, but generally ranges from about 800 to about 850 F. This limitsthe maximum temperature to which the coke can be preheated, however,significant reduction in coke shattering can still be achieved. Althoughthe imum value, it must, on the other hand, be sufficiently high toinsure that the gas exiting the preheater has a temperature which isabove its water condensation temperature, generally above about 180 F.and, preferably, above about 230 F., again to avoid excessive depositionin the equipment.

The temperature of the combustion gases withdrawn from the aflerbumer isgreater than the maximum allowable temperature of the gas which can beinjected into the preheater and, thus, some of the preheater gaseffluent which has been cooled by the coke during its passage throughthe preheater must be recycled and combined with the afierburnercombustion gases to reduce their temperature. Generally the amount ofpreheater exit gas which must be recycled for the appropriate cooling isapproximately three times the amount of afierburner combustion gm whichis introduced into the preheater.

The necessity to maintain a low temperature of the gases introduced intothe preheater and to maintain the gas effluent from the preheater aboveits condensation point limits the temperature differential available foreffecting the preheating. Consequently, large volumes of gas must becirculated through the preheater to raise the coke to the desiredtemperature without reducing the coke flow rate through the preheater.'Ihis gas is recycled by a centrifugal fan which was designed foroperation at about 1,200 revolutions per minute. It has been found thatthis speed is excessive and results in rapid failure of the fan bearingswhen deposits of coke are formed on the fan by the coking precursors inthe recycle gas stream Reduction in speed of the fan, while extendingoperat ing time for the preheater, results in a reduced feed ratethrough the preheater.

We have now found that the preheater can be successfully employed with acoke calcining process without limiting the production rate of theprocess by the use of a recycle gas fan having a sufficient capacity tocirculate from 700 to L000 standard cubic feet of gas per minute (SCFM)per ton of raw coke or about 930 to 1,300 SCFM per ton of calcined cokeproduct at relatively low impeller speeds such as from 800 to l 100revolutions per minute. At these low speeds, imbalances caused by cokedeposition on the fan are not serious enough to require frequentinterruption of the process for cleaning and repair.

The invention will be described with reference to the following figuresof which:

FIG. I is a side view of the preheater, afterbumer and calciner andshows the coke and circulating gas flow; and

FIG. 2 is a cross-sectional view of the preheater taken along line 2-2of FIG. 1.

Referring now to FIG. 1, the coke treatment facilities are shown ascomprising a coke preheater l0, afterbumer l2, and coke calciner 14. Rawpetroleum coke, which is received from a delayed coking unit of apetroleum refinery, is classified into a suitable size range forcalcining and preheating. Particles which are so small that they willresult in an excessive pressure drop in the gas flow through thepreheater are separated. Typically, particles having diameters ofone-eighth inch or less are separated and, preferably, particles havingdiameters of onefourth inch or less are separated. The particles havinga diameter greater than one-fourth inch are thus separated from thefiner particles and are discharged onto conveyor 16. The coke istransported by conveyor 16 to the top of the preheater where it isdischarged into distributor 18. This distributor comprises a conduitwhich narrows at its base and splits into two smaller conduits 20 and22. A gate 24 is pivotably supported to move between positions whichdivert the coke flow into one or the other of the conduits 20 and 22.Each of the smaller conduits is connected to the top of the preheaterthrough serially connected first and second feed traps 26 and 28 andslide gate 30. The feed traps provide a double lock chamber throughwhich the coke may be transferred without allowing air to enter thepreheater. These chambers are ted by trap doors 23 and 27 that aresupported inside temperature of the incoming gas must not exceed themaxthechambers andare pivotable between open and closed posi- IOI0450150 tions. Movement of the doors is effected by air pressure asdescribed in greater detail hereinafter with reference to FIG. 2. Theslide gates 30 are horizontal, impermeable plates which, when closed,slide over the entrances to the preheater and seal the preheater fromthe feed traps. Each slide gate is biased with a closing force such as apneumatic ram actuated by air pressure. The slide gates are open whenfilling the preheater and, in the event of a power failure, or a failurein the air pressure to gates 23 and 27, these slide gates 30 will closefrom the air pressure available in an air reservoir, thereby retainingthe preheater isolated from the atmosphere.

The preheater to, which is shown in greater detail in FIG. 2, comprisesvemel 32 which contains a gravitating bed of coke solids. Baffle means,internally positioned in preheater l distribute the coke to a heattransferring section at the base of the preheater where the coke iscontacted by hot combustion gases introduced therein through conduit 36.The hot gases are distributed throughout the coke bed in the heattransferring section by a gas distributing means. The gases pass throughthe coke bed and are collected within the preheater by a baffledcollecting means and are finally removed from preheater through conduit34.

The coke solids are discharged from the preheater by hydraulicallyactuated rams which force the coke into discharge hopper means 38 andconduit 40. Conduit 40 discharges the coke directly into the rotary kiln14. The ram mechanisms for forcing the coke into discharge hopper 38 areshown in end view together with coke collection means for retaining anycoke which spills behind the rarm during their forward motion and whichis pulled from the bed when the rams are retracted. This backspill cokeis collected in hoppers 37 which are connected by inclined conduit 39 tostandpipe 4!. This standpipe discharges the coke into a screw conveyor43 which has a water seal to prevent air leakage into the preheater. Thescrew conveyor thereafter transfers the coke particles to conduit 40 andkiln 14 through line 45.

The coke is calcined in kiln 14 by contacting the coke therein with hotcombustion gases. The kiln is rotated at a velocity to achieve aresidence time of the coke in the kiln of about 50 to about 58 minutes,preferably about 54 minutes. The kiln combustion gases are generated byburner 42 which is supplied with air from fan 44 and fuel such asmethane through line 46. Air is directly injected into kiln 14 throughauxiliary fan 48 which maintains a sufficient amount of air within thekiln to burn a portion of the volatile combustible material released bythe coke during calcination. The amount of air injected into the kiln byfan 48 is also controlled so as to maintain the gas temperature exitingthe kiln between about 1,000 and l,200F.

The coke is discharged from the revolving kiln through a stationary hood50 maintained at the rear of the kiln. A seal is maintained between hood50 and calciner l4 and cooled by circulating cooling air through jacket54 which encircles the seal. The colling air is supplied to coolingjacket 54 by fan 56. The hood is a refractory lined housing whichencorrmasses the end of kiln l4 and achieves the calcined coke exitingthe kiln drum. The bottom of the hood is connected to a rotary cokecooler through conduit 52 to allow coke to discharge directly from kiln[4 through hood 50 and conduit 52 into the coke cooler, not shown.

The hot gases exit kiln 14 through opening 60 at the coke inlet end ofkiln l4 and discharge directly into afterburner 12. The afierbumer I2 isa stationary, refractory lined vesel with one end thereof connected tothe coke inlet end of kiln 14. As the gases enter this vessel from thekiln they pass over dam means 58 which is an annular baffle formed ofrefractory bricks and peripherally mounted within aflerburner l2 andextending radially inwardly a sufficient distance to shield the steeltail ring of kiln 14. This refractory dam shields kiln l4, and, inparticular, tail ring 62 of kiln 14 from radiation of the gases inafierburner 12 and thereby avoids warping of this steel ring andresultant failure of its refractory lining.

The hot gases in after-burner 12 are crmtacted with air that is forcedtherein through several tangential jets circularly located around theafierbumer. A circular plenum formed by bussle ring68 en the afierbumerand bears tangential jets 69 through which air is forced by fan 66 andconnecting conduit 64. The air, entering tangentially into theafterburner, creates vortices within the chamber and improvesintermixing of the gaseous constituents. A sufficient amount of air issupplied to the afterburner to insure nearly complete combustion of allcombustible material in the gases. The resultant combustion generallyraises the temperature of the gases to about 1,500 F.

a portion of the gases in afterburner 12 is discharged through dampermeans 70 into a refractory lined, pyrolytic scrubber 72. The dampermeans 70 comprises a refractory lined plate which when fully insertedinto the afierburner isolates the afterburner from the pyrolyticscrubber. The amount of gases vented to the scrubber can be adjusted bysimply raising or lowering damper means 70. Air is injected into thescrubber 72 from line 74 and fan 76. Line 74 passes through preheater 10so as to cool the internal preheater baffles and raise the temperatureof the air passing therethrough to about 150 F. An excess of air isinjected into the scrubber so that all of the unburned volatile materialis completely combusted along with any coke particles which my beentrained in the exiting afterburner gas stream. The purified gases aredischarged into the base of exhaust stack 78 through a refractory linedbreeching 80.

The remainder of the afterbumer gases is pulled through large diameterduct 36 to the preheater. A butterfly type damper 82 is disposed withinduct 32 to provide means for isolating the preheater 10 from theafterburner 12 when shutdown of the facilities is necessary. After thehot gases contact the raw coke in the preheater, they are removedthrough duct 34 and drawn into the intake of a large circulating fan 84.A slide gate 86 is maintained wifl'iin this duct to isolate thepreheater from the afierburner during shutdown. The circulating fandischarges the gases to two locations; a portion is passed directly intothe afierburner through line 88 which enters at the side of thealterbumer so that particles in the afterburner cannot fall into theline when the fan is shut down, and the remainder of the gases isdischarged through line 90 into duct 36 with the relative amounts andportions of the preheater gases being controlled by damper 92.

The damper 92 is adjusted so that the amount of gas recycled to thepreheater is sufficient to maintain the temperature of the gas enteringthe preheater between about 800 and 8 50 F., below the temperature atwhich any objectionable amount of volatile combustible material isreleased by the raw coke. This temperature will vary somewhat, dependingon the coke source and type. The maximum temperature which can be usedcan be determined for any particular coke by a thermogravimetricanalysis and selecting the temperature to be no greater than that whichwill volatilize about 1 percent of the total volatile combustiblematerial from the coke.

The preheating of the incoming raw coke with circulation gas having theproper temperature requires the use of large volumes of recyclepreheater gas, and fan 84 must therefore be adequately sized forhandling the large volumes of circulation gas. It has been found thatfor an incoming preheater gas temperature within the desired range, thegas rate should be from 3,000 to 4,000 pounds per hour per ton of rawcoke.

Some volatile combustible material (VCM) can be released from the cokein the preheater as well as minor amounts of small particulate coke.These volatiles and fine particles are entrained within the circulatinggas and form coke deposits on the various surfaces contacted by the gas.The coke deposition is the greatest on the bafiles and obstructionswhich are directly impinged by the gas stream, such as on the blades offan 84 and on damper 86. Coke deposits are also often found within lines34 and 90 and, particularly, at each bend or curvature in these lines.Of particular importance is the necessity of maintaining fan 82relatively free of coke buildup since minor imbalances on the fan bladescause severe fan vibrations and necessitate preheater shutdown for fancleaning. It has been found that successful operation of the preheaterover extended run periods requires that the fan 84 be massivelyoversized with enlarged shaft and sleeve bearings to withstand min rorimbalances from coke deposits. It has also been found that the fan mustbe operated at relatively low rpm, e.g., SOD-l ,100 rpm, since at lowrpm the fan can withstand minor vibrations over prolonged periods. Thefan housing should also be provided with quick opening doors that can beopened to permit cleaning of the housing and fan blades.

Successful operation of the preheater also requires that all gascirculation lines and dampers be sized for minimum flow resistance. Thepreheater is designed for minimum pressure drop through the coke bed atthe aforementioned flow rates, e.g., about 12 to l8 inches of water. Thepressure drop through line 34 to the fan is about l to 3 inches ofwater.

The preheater is illustrated in more detail in FIG. 2 which is across-sectional view taken along line 22 of HG. l and displays theintemal components of the preheater. An A-shaped bafi'le 100longitudinally traverses the lower center of the preheater and extendsfrom one side of the preheater to the other. The baffle 100 is supportedwithin the preheater by refractory lined support columns 101 whichvertically extend from the preheater base 118 and connect with each legof the baflle. Cooling tube 102 pass through the center of each supportcolumn 101 and connect with each leg of the baffle. These cooling tubesprovide a means for cooling the baflle and supports during operation ofthe preheater. The baffle is protected by refractory bricks 104 whichline the lower half of the baffle exposed to the hot circulating gases.A triangular passageway 103 passes through the preheater and upperportion of baffle 100 and communicates wifli the atmosphere. Thispassageway is fluid-tightly sealed from the internals of the preheaterso as to prevent air from entering the preheater. A cooling line 106 islongitudinally disposed within triangular passageway 103 andcommunicates with the upper portion of ballle 100. This line provides acooling means for the upper parts of the baffle by circulating airtherethrough from an externally located fan shown as 76 in FIG. 1. Theair passes through the battle and is removed through line 74 shown inFIG. 1 which discharges the heated air into pyrolytic scrubber 72.

A gas distributor 108 is disposed immediately beneath A- shaped baffle100 and longitudinally extends the length of the baffle and preheater10. The distributor comprises a permeable conduit with one end sealedagainst one side of the preheater wall and the other end extendingthrough the opposite side of the preheater and connecting to gas conduit36. The hot combustion gases from the afterbumer enter the preheaterthrough the gas distributor 108 and pass through the coke around thebase of the A-shaped baflle 100.

The gas, after contacting the coke around the base of baffle 100, iscollected by a baffled collecting means located above the gasdistributor I08 and removed from the preheater by conduit 34. Thecollecting means comprises baffle plates 110 which are longitudinallydisposed along each side of the preheater wall above A-shaped conduit100. Each baffle plate is inclined downwardly towards baffle 100 to forma longitudinally disposed inverted V-shaped enclosure between the baffleplate and wall of the preheater. A short skirt 112 on each baffle platetowards the legs of the A-shaped baffle 100 and constricts the areabetween the bafile 110 and the legs of baffle 100. A permeable duct 114is located under each baffle plate "0 within the V-shaped enclosure andextends longitudinally the length of the baffle. One end of eachpermeable duct 114 is connected to efiluent conduit 34 through a cornmonheader, not shown, and the other end terminates at the wall of thepreheater. The baffle plates 1 as well as the skirts 112 are refractorylined for protection from the hot circulating gases.

The preheater is equipped with hydraulic rams which push the particulatecoke under the leg of bafi'le 100 and into a discharge hopper 38. Thehydraulic rams 116 extend through wall 32 on each side of the preheaternear the refractory lined preheater base 118. Each ram is comprised of ahydraulic cylinder 120 and associated piston, housing seal 124, push rod126 and ram piston 130. The seal 124 is a rubber sleeve that is securedat its opposite ends to the hydraulic cylinder 122 and to the outsidewall of hopper 37 so that air is precluded from leaking through thesliding joint around rod 126. The rams 1 16 are disposed at a slightangle from horizontal so that when ram piston is extended it movesdownwardly along slide plate 132 towards the center of the preheater anddischarge hopper 38. The actuation cylinders 122 as well as seal 124 arelocated outside the preheater walls with push rods 126 extending throughspill hole 134 in preheater wall 32 to the ram piston 130 within thepreheater. The lower portion of the preheater is lined with refractorybricks 136. The ram pistons 130 are stainless steel.

During the forward motion of ram 116, a portion of the particulate cokefalls behind ram piston 130, between the back of the piston andpreheater wall. When the piston is retracted, the ram discharges thiscoke through hole 134. Hoppers 37 are connected to the outside of thepreheater around ram l 16 to collect the coke forced through hole 134during the retraction period. The hoppers are sealed around holes 134 soas to prevent air from entering the preheater. The hoppers are connectedto an inclined conduit 39 and standpipe 4! shown in FIG. I.

Coke is introduced into the preheater through a set of first and secondfeed traps 26 and 28 and slide gate 30. The feed traps when connected inseries, as shown in FIG. 2, provide a double lock chamber through whichthe coke can be transferred to the preheater without allowing anysignificant amount of air to enter the preheater. Each feed trapcomprises a rectangular chamber which has a large cross-sectional areanear the top and which tapers inwardly to a smaller crosssection nearthe bottom of the trap. The feed conduit 20 projects into the top offirst trap 26 for a short distance and is completely encompassed bychamber 140. The tapered bottom of the trap projects into the top of thesecond trap 28 and is similarly encompassed by chamber 142 of feed trap28. 'lhe bottom of feed trap 28 discharges into the top of the preheaterthrough slide gate 30. A trap door 23 closes against the bottom ofconduit 20 and seals chamber 140 from the conduit. Similarly, trap door27 closes against the bottom of feed trap 26 and seals chamber 142 fromchamber 140. These trap doors 23 and 27 are respectively connected bycrank means 148 and 150 to pneumatically actuated cylinders 152 and 154so that when the pistons are retracted in these cylinders, the trapdoors are opened, allowing communication between the preheater andconduit 20. These trap doors are sequentially operated so that when trapdoor 27 is closed and chamber I42 is isolated, trap door 23 can beopened and chamber 140 can be filled with coke. When trap door 23 isclosed, trap door 27 is opened, thereby allowing the coke in chamber I40to empty into the preheater. With the sequential operation of the trapdoors, the coke can be delivered to the preheater with a minimum influxof air.

As previously mentioned, slide gate 30 is disposed between feed trap 28and preheater 10 to provide means for isolating the preheater from thefeed traps. Slide gate 30 comprises a horizontal impemteable plate 156which, when closed, seals the entrance to preheater 10. The slide gate30 is actuated with a pneumatic cylinder and piston assembly which issupplied with air under pressure from an air reservoir. Any failure inthe actuating pressure which results in a simultaneous opening of bothtrap doors 144 and 146 also results in an automatic closing of slidegate 30, thereby maintaining preheater l0 isolated from the atmosphere.

In operation, particulate coke having a mean diameter greater thanone-fourth inch and a size range from one-fourth to about 6 inches isconveyed to the preheater and discharged into feed conduit 18.Sequential operation of dividing gate 24- and feed traps 26 and 28 fillspreheater 10 with coke. The

filling procedure continues automatically until the preheater iscompletely filled and the coke contacts level indicator 160 whichinterrupts the filling procedure. The coke flows downwardly withinpreheater through the constricted area between baffles 100 and 110 andforms a compact bed of solids beneath skirted baffle 1 10. The coke isforced under the legs of A-shaped baffle 100 towards the center of thepreheater by rarm 116. Simultaneously with the flow of coke through thepreheater, hot combustion gases are introduced into the preheater fromgas distributor 108. These gases pass around the bottom of the A-shapedbaffle and up through the coke bed to gas collector 114. During the timethe coke is preheated, generally between about 35 and 50 minutes, thecoke temperature is raised from ambient to approximately 600 to 700 F.and almost all of the water contained within the raw coke (between about8 and I2 weight percent) is vaporized and removed with the effluent gas.

The coke forced to the center of the preheater by rams 116 falls intohopper 38, through conduit 40 to kiln 14. During the retraction periodof the pneumatic rarm a small portion of particulate coke is trappedbehind the retracting ram piston 130 and forced into discharge hoppers37. The coke in the hopper 37 falls through conduit 41 by gravity toscrew conveyor 43. The screw conveyor has a water seal of from 4 toabout 12 inches of water to prevent any introduction of oxygen into thepreheating apparatus. The coke is transported from the screw conveyorand discharged through conduit 40 to kiln 14. The coke after droppinginto the kiln contacts hot combustion gases which exit from the kiln atabout l,000l ,200" F. The coke is calcined within the rotary kiln forapproximately 50 to 60 minutes at which time the coke temperatureincreases to about 2,000 F. to 2,400 F. At these conditions almost allof the volatile combustible materials have been driven out of the cokeand are partially combusted in the kiln. The amount of volatile materialcombusted in the kiln is controlled by the amount of air introduced intothe kiln from fan 48 which is operated to control the temperature of thecombustion gases exiting the kiln at the aforestated range and,preferably, at about 1,000 F. The calcined coke falls from kiln 14through hood 50 and conduit 52 into a forced drafi, rotary cooler wherethe coke particles are water cooled to about 300 F.

The combustion gases exiting from the kiln have temperatures which rangefrom 800 to about [200 F. These gases are passed directly intoafterbumer 12. In the afterbumer, the gases are mixed with air and aportion of the unburned volatile material released from the coke in thekiln is burned. The combustion in the afterburner raises the temperatureof the gases to about L500 to 1,800 F. A portion of the resulting hotgases is then pulled into pyrolytic scrubber 72 where it mixes with anexcess of warmed air and the mixture burned to remove any remainingvolatiles and entrained coke particles in the gases. The remainingportion of the hot combustion gases is mixed with a large volume of coolrecycle gas from the preheater to reduce the temperature of the gasstream to about 800 to 850 F. This gas stream is then injected into thegas distributor 108 within the preheater 10. The gas effluent is removedfrom the preheater through collector 114 and conduit 34. A portion ofthis gas effluent is recycled and the remainder is injected into theafterburner.

The invention is further illustrated by the following example which isillustrative of a specific mode of practice of this invention and whichis not intended as limiting the scope of the invention as defined by theappended claims.

EXAI'VIPLE This example demonstrates the improvement of preheating cokeprior to calcination in accordance with this invention. In this exampleseveral runs are conducted to illustrate the criticality of operatingthe preheater under the proper conditions.

A preheater is constructed as substantially shown in FIG. 2 andinstalled in combination with an afterburner and rotary kiln as shown inFIG. 1. The kiln is 9 feet in diameter and feet long and is placed at aslightly downward incline to permit the incoming coke to pass to thedischarge end of the kiln within about 54 minutes at the design capacityof 15 tons per hour of calcined product coke. The aflerburner is 30 feetlong and has a diameter of approximately 9% feet. The preheater isrectangular in shape having a width of 28 feet, depth of 18% feet and aheight of approximately 30 feet. The inlet conduit 36 connecting theafter burner with the preheater has a diameter of 4.67 feet, and thepreheater efiluent conduit 34 has a diameter of about 3.67 feet. Thecirculating fan 84 has an operating capacity of about 28,000 cubic feetper minute at l ,000 rpm.

in each of the runs, about 20 tons per hour of raw coke having aparticle size between one-fourth inch and 6 inches are charged into thepreheater through the double lock feed traps. The raw coke containsapproximately 10 weight percent moisture and 14 weight percent ofvolatile combustible material.

The hot combustion gases which are circulated through the preheater areinitially generated in the kiln by burning in the kiln, approximately400 pounds per hour of methane and 27,000 pounds per hour of air. Thetotal amount of air injected into the kiln is controlled so that thetemperature of the gases exiting the kiln is maintained at about 1,100F. Approximately 27,000 pounds per hour of air are injected into theafterbumer to raise the gas temperature to about L600 F.

A portion of the hot afterbumer gases, approximately 20,000 pounds perhour, is withdrawn from the afterburner and mixed with a sufficientamount of recycle, preheater effluent gas to reduce the temperature ofthe gas mixture to about 800 F. This gas mixture is pulled into thepreheater, which is under negative pressure, and forced through the bedof particulate coke. The gas effluent is withdrawn from the preheater byfan 84 and approximately two-thirds of the effluent stream is recycledto the preheater inlet gas stream. The remaining third of the gaseffluent is discharged into the afterburner.

The kiln, afterburner and preheater are operated at subatmosphen'cpressure which is achieved by the draft from the stack. During operationthe following pressures exist at the indicated locations:

When the preheater facilities are operated at the above rates andconditions, it is found that the coke leaving the preheater isapproximately 650 R, which is sufficient to reduce significantly theamount of shattering of the particulate coke in the kiln. It is foundthat operation of the preheater-kiln facilities can be conducted overprolonged periods without shutdown of the preheater for cleaning orrepair.

When the preheater is operated at the above rates and conditions exceptthat the inlet temperature of the gas mixture discharged into thepreheater is maintained at 1,500 F., it is found that the coke leavingthe preheater has a temperature of about 1,000 F. At these conditions,however, successful continuous operation can not be attained because theequipment rapidly becomes laden with coke deposits and the process mustbe interrupted after about 4-5 days to clean and repair the equipment.

Although we have illustrated the present invention in connection withspecific embodiments thereof, it is not intended that the illustrationsset forth herein shall be regarded as limitations on the scope of theinvention, but rather, it is intended that the invention be defined bythe steps set forth in the claims and their equivalents.

We claim:

1 in the method of preheating and calcining particulate petroleum coketo produce calcined coke in a preheater and kiln that are maintained atsubatmospheric presure, wherein hot gases from calcination of said cokein a calciner kiln are mixed with air and combusted in an afterburner toobtain combustion gas having a temperature of from 1,500 to 2,000 E, anda portion of the combustion gas is introduced into a preheater vemelcontaining said petroleum coke and pamed therethrough in contact withsaid coke to heat said coke to a temperature geater than 600 F. andwherein effluent gases are withdrawn from said preheater, repressured bya fan, and a portion thereof is recycled and mixed with said combustiongas from said afterburner to obtain a preheater hot gas stream having atemperature of 800 to 850 F., the improvement comprising: passing saidcoke through said preheater and said kiln at a rate sufficient tomaintain a residence time of coke in said kiln from to about 58 minutesand passing said pre heater hot gas stream through said preheater at aflow rate of from 930 to about 1,300 standard cubic feet per minute perton of product calcined coke and sufficient to maintain the temperatureof said effluent gases above about 200 F.

2. The method defined in claim 1 wherein air is supplied to the inlet ofsaid kiln to control the temperature of said gases from the kiln betweenabout 1,000 and 1,500 F.

3. The method defined in claim I wherein from 50 to 75 percent of theeffluent gases from said preheater are recycled and mixed with saidportion of said combustion gases from the afierburner.

4. The method defined in claim 1 wherein said particulate calcinedpetroleum coke is separated to obtain a particle size greater thanone-fourth inch.

5. The method defined in claim I wherein the temperature of saidefi'luent gases is maintained above about 250 F.

6. The method defined in claim 1 wherein said fan is operated at a speedof from about 500 to about l,l00 revolutions per minute.

7. The method defined in claim 1 wherein said coke is introduced intosaid preheater while excluding air from entering said preheater bytransferring said coke through a plurality of serially connectedchambers which are intermittently and alternately opened and closed.

8. The method defined in claim I wherein said coke is discharged fromsaid preheater by reciprocating rams to discharge the coke into saidkiln and wherein air is precluded from entering the preheater byflexible sealing means maintained about said rams.

9. The method of claim I wherein coke particles which are pulled fromsaid preheater by said ran's during their rearward movement is collectedby means sealed to the atmosphere and recovered by passage through awater seal that prevents air entry into said preheater.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION July 18, 1972Patent No. 3 6 77 5 33 Dated cofl Robert K. Oliver and George L. Ford Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

On the Abstract page, two occurrence s,

"Olover" should be Oliver Signed and sealed this 2nd day of January1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Commissioner of PatentsAttesting Officer USCOMM-DC O0376-P69 FORM PO-IOSO (IO-69] u s sovnnulmnmmuc. ornc: 19" 0-3ee-u4

2. The method defined in claim 1 wherein air is supplied to the inlet ofsaid kiln to control the temperature of said gases from the kiln betweenabout 1,000* and 1,500* F.
 3. The method defined in claim 1 wherein from50 to 75 percent of the effluent gases from said preheater are recycledand mixed with said portion of said combustion gases from theafterburner.
 4. The method defined in claim 1 wherein said particulatecalcined petroleum coke is separated to obtain a particle size greaterthan one-fourth inch.
 5. The method defined in claim 1 wherein thetemperature of said effluent gases is maintained above about 250* F. 6.The method defined in claim 1 wherein said fan is operated at a speed offrom about 500 to about 1,100 revolutions per minute.
 7. The methoddefined in claim 1 wherein said coke is introduced into said preheaterwhile excluding air from entering said preheater by transferring saidcoke through a plurality of serially connected chambers which areintermittently and alternately opened and closed.
 8. The method definedin claim 1 wherein said coke is discharged from said preheater byreciprocating rams to discharge the coke into said kiln and wherein airis precluded from entering the preheater by flexible sealing meansmaintained about said rams.
 9. The method of claim 1 wherein cokeparticles which are pulled from said preheater by said rams during theirrearward movement is collected by means sealed to the atmosphere andrecovered by passage through a water seal that prevents air entry intosaid preheater.